This is my second post.......
I have a 98 S10 Blazer, with a 4.3L, and I have had a continuing issue with when changing out of 2Hi into either 4Hi or 4Low, both the 4Hi/4Low lights stay illuminated on the 4WD switch. It will go into 4Low, and only momentarily into 4Hi before disengaging - it sounds like it goes into 4Hi, the motor actuates, but goes right back into 2Hi. Any thoughts?

 

sounds like a sensor issue, possibly the front axle detend switch? are your vacuum lines and net manifold vacuum pressures good?

 

Yes, I have 17-18' of steady vacuum. So you are referring to the switch that is mounted on the front differential?

 

Odd, Is the vacuum hose to the pull-cable actuator under the battery good? And is the solenoid on the firewall engaging.

 

yes I replaced the vacuum actuator, the cable, and that mechanical solenoid that bolts into the differential - I replaced all three of them. And when you ask about the solenoid are you talking about the control module on the right side kick panel? If so, it has also been replaced. But I have not yet replaced that switch that’s part of that four-wheel-drive solenoid mechanism on the front differential.

 

that last switch is the one im talking about, the axle detent switch is what tells the TCCM that the front axle has engaged, try R&R or a basic Ohm-out of that switch on the bench.

 

I replaced the vacuum hose to the actuator, and I do not have a solenoid on the firewall. Also, I have verified that the spring and shifting fork work correctly.

Here is another interesting fact, it will go into low range and the 4wd works, but it will not go into 4hi.

 

Wait so 4lo Works? Ok so now we need to have a look at the Tcase, Im going to assume you have a 3 button Controller, you said you've already replaced the TCCM so now we need to look into the shift motor on the Tcase and the dash controller itself,i cannot remember if the Tcase motor is controlled by or reports back serial data or dry voltage signals so someone with factory data or service info hopefully will chime in.Given that the parts cannon has been fired well in advance the goal would be to reduce the amount of guesswork.

 

Well I have also replace the encoder motor and the transfer case control module on the left kick panel……..also, I can hear the encoder motor actuate when I push the 4low button, and it takes a second or two, but I also hear it shift into 4hi…….?

 

its almost like its missing its gear, or cant detect that its in what gear it thinks its in.